Informations about the MicrosoftCryptoAPI is available online on the Microsoft MSDN at http://msdn.microsoft.com/library/en-us/seccrypto/security/cryptography_portal.asp.
You can also download the Microsoft Platform SDK for Windows Server 2003 R2 or later version without charge. This developer kit contains all the documentation about CryptoAPI (search in the contents for Security, and then Cryptography).